The U.S. military has airdropped weapons, ammunition and medical supplies to Kurdish fighters in the Syrian city of Kobani to beef up the defense against ISIS forces, the Pentagon said.

"The aircraft delivered (items) that were provided by Kurdish authorities in Iraq and intended to enable continued resistance against ISIL's attempts to overtake Kobani," the U.S. Central Command said Sunday.

(The administration refers to the group as ISIL, the acronym for "Islamic State of Iraq and the Levant." CNN refers to it as ISIS; the group recently started calling itself the Islamic State.)

The move was partly humanitarian but also aimed at shoring up the Kurdish defenders of Kobani, senior Obama administration officials said - acknowledging it was a shift in the administration's tactics to date.

"This is a part of the President's larger strategy to degrade and destroy ISIL wherever they are," one official said.

The gear was delivered by three C-130 cargo planes and appeared to have been received on the ground by Kurdish fighters, senior Obama administration officials.

There have been reports that ISIS may have anti-aircraft missiles, but the officials said they had no evidence to back those reports and that the cargo planes flew in unescorted.

The key Syrian border city of Kobani will soon fall to ISIS, but that's not a major U.S. concern, several senior U.S. administration officials said.

If Kobani falls, ISIS would control a complete swath of land between its self-declared capital of Raqqa, Syria, and Turkey - a stretch of more than 100 kilometers (62 miles).

The U.S. officials said the primary goals are not to save Syrian cities and towns, but to go after ISIS' senior leadership, oil refineries and other infrastructure that would curb the terror group's ability to operate - particularly in Iraq.

Saving Iraq is a more strategic goal for several reasons, the officials said. First, the United States has a relationship with the Iraqi government. By contrast, the Obama administration wants Syrian President Bashar al-Assad to step down.

Another reason: The United States has partners on the ground in Iraq, including Iraqi forces and Kurdish fighters known as Peshmerga.

But on Tuesday, a top U.N. official implored world leaders to take action as Syrian Kurdish fighters defending Kobani are dangerously outmatched.

"They have been defending themselves with great courage. But they are now very close to not being able to do so," said Staffan de Mistura, the U.N. special envoy for Syria.

"They are fighting with normal weapons, whereas the ISIS has got tanks and mortars," he said. "The international community needs to defend them. The international community cannot sustain another city falling under ISIS."

The United States is doing what it must to "take the fight to terrorists," leading a coalition of Arab nations in a series of airstrikes against the so-called Islamic State terror group in Syria, U.S. President Barack Obama said Tuesday.

At the same time, the United States took action - on its own - against another terrorist organization, the Khorasan Group. Obama described its members as "seasoned al Qaeda operatives in Syria."

U.S. officials said the group was plotting attacks against the United States and other Western targets.

The plots against the United States were discovered by the intelligence community in the past week, an intelligence source with knowledge of the matter told CNN. The source did not say what the target may have been, but said the plot potentially involved a bomb made of a nonmetallic device like a toothpaste container or clothes dipped in explosive material.

A plot involving concealed bombs on airplanes "was just one option they were looking at," a U.S. official said.

"Once again, it must be clear to anyone who would plot against America and try to do Americans harm that we will not tolerate safe havens for terrorists who threaten our people," Obama said in televised remarks from the White House.

Concern over a possible backlash by the terror groups has prompted the U.S. Department of Homeland Security to issue a bulletin warning law enforcement agencies to be on heightened alert for lone-wolf terror attacks on U.S. soil in wake of the airstrikes, a U.S. law enforcement official with knowledge of the warning told CNN.

The bulletin calls for vigilance as well as scrutinizing social media for anyone encouraging violence in response to the strikes, according to a U.S. law enforcement official with knowledge of the warning's contents. It points to the use of social media as a tactic by ISIS to spread its message and call for violence.

It also advises agencies to look for changes in appearance or behavior in those they're tracking, the official said.

One by one, Iraqi cities seem to be falling to a militant group bent on continuing its march forward.

What's happening in Iraq now has all the makings of a civil war - and a full-blown foreign policy crisis. The United States is mulling direct talks with Iran while it boosts security at the U.S. Embassy in Baghdad with military personnel.

Why Iran? In recent days, Iran has sent hundreds of troops to fight alongside Iraqi government security forces in Diyala province, a senior security official in Baghdad told CNN.

Clearly, the crisis in Iraq is spilling far beyond its borders. Here's the latest:

Iraq's military strikes back at ISIS

After days of violent advances by the militant group ISIS, the Iraqi air force killed more than 200 militants from the Islamic State in Iraq and Syria, Iraqi state TV reported Monday.

The air raids against ISIS took place in Saqlawiya, northwest of Falluja, according to state TV.

ISIS has been fighting to take control of Iraq, seizing cities across the country.

Iran enters the mix

In recent days, Iran has sent about 500 Iranian Revolutionary Guard troops to fight alongside Iraqi government security forces in Iraq's Diyala province, according to a senior security official in Baghdad who spoke to CNN on Friday.

But Iranian President Hassan Rouhani denied reports that some of Iran's elite forces are in Iraq to help bolster Iraqi Prime Minister Nuri al-Maliki, a fellow Shiite.

"If the Iraqi government wants us to help, we will consider it," Rouhani said, according to an English translation of his remarks Saturday on state-run Press TV.

But "so far they have not asked specifically for help." Rouhani added that Iran could give strategic guidance if requested.

The Obama administration is exploring possible direct talks with Iran over the deteriorating situation in Iraq, two senior U.S. officials told CNN.

Both officials ruled out any type of teaming up with Iran because the United States and Iran don't have a lot of common interests - other than a stable Iraq.

The United States is wary of furthering Iran's already considerable influence in Iraq. The Shiite Iranian regime is al-Malaki's closest ally in the region. And the Obama administration is concerned appearing to team up with Iran would both alienate Iraq's Sunni majority and worry Sunni allies of the United States in the region.

Thirteen nuns and three workers kidnapped in late November from a Greek Orthodox monastery in Syria were freed Sunday, a pro-Syrian government news network and Lebanese state media reported.

A convoy of around 30 vehicles picked up the nuns and workers in one part of Syria and took them into Lebanon, the country's National News Agency reported late Sunday. The convoy traveled through Lebanon to another border crossing into Syria, the hillside village of Jdaidet Yabous. There, the group will be met by Greek Orthodox church officials, who will welcome them back into Syria, Syrian state news agency SANA reported.

The convoy was at one point delayed several hours for "logistical reasons" but later resumed en route to Jdaidet Yabous, Public Security Director Gen. Abbas Ibrahim told NNA.

When they did arrive overnight, the nuns - some smiling, some solemn and at least one of whom appeared to be being carried - were mobbed by an enthusiastic crowd that included church officials.

Ibrahim said that no money was paid to secure the release of the nuns, adding that it was part of a deal in exchange for 150 females that the Syrian government was holding.

Qatari intelligence chief Saadeh Kobeisi reportedly crossed deep into Syrian territory to obtain the release of the Syrian nuns. He crossed into Syria as part of a Lebanese Internal Security delegation, the state news agency said.

Senior Orthodox Bishop Lucas al-Khoury earlier Sunday spoke to pro-Syrian government Ikhbariya television. He stood on the Syrian side of the border hoping to greet the nuns and said the negotiations for their release took several months because the kidnappers "made false requests intended to stall the process."

World leaders gathered this morning at a conference in Switzerland that has been billed as possibly the best chance for ending the war in Syria.

It is the first time the Assad regime and opposition will meet face-to-face with officials from dozens of other countries.

But it’s notable who is not there- Iran- and there are real questions if the conference will accomplish anything at all. Based on Nic Robertson’s update, things do not seem promising:

“Not a lot, if any, conciliation coming from the Syrian government side. Then we heard from Secretary of State John Kerry unequivocally, and very clearly, say that Bashar al-Assad cannot be any part of this process going forward.”

U.N. inspectors will release their official report Monday on the use of chemical weapons from an August attack in Damascus, Syria. CNN's Nick Paton Walsh reports.

United Nations Secretary General Ban Ki-moon may have thought he wasn't on camera Friday when he said this of today's vital report:

"I believe the report will be an overwhelming report that chemical weapons were used even though I cannot say publicly at this time."

The U.N. leader added Syrian President Bashar al-Assad had committed many crimes against humanity and would eventually face a "process of accountability."

One official tells Walsh it's likely the report was complete by that meeting and Ban Ki-moon may have already seen the findings before giving his statement.

The U.N. inspectors report on the August 21st gas attacks will be presented to the security council at 11 a.m. in enough detail for others to work out who was behind the attacks, though it's not the inspectors job to do so.

The U.N. says Syria now has officially joined the chemical weapons convention, whose rules mean it must declare all those weapons by mid-November.

That's not fast enough for the United States or Russia who agreed in Geneva, Switzerland, that Syria must tell reveal their weapons in a week.

In Syria's first major comments on the deal, its information minister told ITV News it wants to wait for a U.N. resolution to set the timing of its disarmament.

Now another round of negotiations begins, perhaps fast, perhaps torturous, to find a wording for a resolution that can back up what was agreed in Geneva last week.

Some major questions remain to be negotiated. A diplomat reveals one major point is: will a U.N. resolution blame Assad and demand a trial for those who ordered the attacks?

He says he hopes his "friends" in Syria bring their chemical weapons under control and also "have them destroyed" but Vladmir Putin's role as the last, best hope for diplomacy in this crisis isn't winning believers in Washington. CNN's Brian Todd reports.

Sen. John Cornyn, a Texas Republican on the Armed Services Committee says, "the Russians are part of the problem in Syria. They are not credibly part of the solution."

This skepticism builds as President Putin writes an open letter in the New York Times saying it is not the Syrian government that should be blamed for the use of chemical weapons in the country. He writes:

"There is every reason to believe it was used not by the Syrian Army, but by opposition forces, to provoke intervention by their powerful foreign patrons."

France says the United Nations will probably publish its report on the August chemical attack on Monday. The country says there will be indications in the report the Assad regime was behind the attack.

Senators Cornyn, John McCain and others have been ticking through laundry lists of why they believe Putin won't follow through on getting the Syrians to give up their alleged chemical weapons.

They cite planeloads of Russian weapons sent to the Syrian regime for hefty profits, nearly $1 billion worth in 2011 alone.

There's also a Russian naval base in Syria.

Julia Ioffe, senior editor at the New Republic, spent three years as a journalist in Russia. She says Putin views his role in the world "to be a counterweight to America."

Though Senator Diane Feinstein and others believe Putin does want to reach a deal to end this crisis and that he doesn't want Syria to have chemical weapons.

Ioffe says Putin wants to be the cause of attention and show President Obama that he has the ability to end this issue peacefully.

The reporter notes the Russian president wants "to be center stage, to be somebody that you reckon with, somebody that you have to come to and seek his approval and you have to come and kiss his ring."

President Obama spoke from the East Room of the White House to the American people and the world Tuesday night in a speech giving his position on Syria. CNN's Brianna Keilar reports.

The President laid out some of his case for military strikes against Syria but also cautiously embraced a Russian plan to try diplomacy first.

First, the commander in chief told Americans why his administration is certain Syrian President Bashar al-Assad's regime is responsible for a sarin gas attack the U.S. government says killed more that 1,400 civilians.

President Obama: In the days leading up to the August 21st, we know that Assad's chemical weapons personnel prepared for an attack near an area where they mix sarin gas. They distributed gas masks to their troops. Then they fired rockets from a regime-controlled area into 11 neighborhoods that the regime has been trying to wipe clear of opposition forces.

While he made the case for a military response saying "even a limited strike will send a message to Assad that no other nation can deliver" later in the speech, he argued against taking action as he pointed to a new Russian brokered proposal for Syria to give up its chemical weapons.

President Obama: I have therefore asked the leaders of Congress to postpone a vote to authorize the use of force while we pursue this diplomatic path.

Keilar says many observers doubt Syria will actually turn over its extensive chemical weapons stockpiles and the administration is concerned the Assad regime may just be stalling.

Secretary of State John Kerry said Tuesday, "It has to be swift, it has to be real, it have to be verifiable. It cannot be a delaying tactic."

The diplomat will head to Geneva, Switzerland, Wednesday to meet with his Russian counterpart Sergei Lavrov Thursday.